1. Field of the Invention
The present invention generally relates to a Visible Light Communication (VLC) navigation system and more particularly, to a method for exchanging messages between a visible light terminal and a navigation server in a navigation system.
2. Description of the Related Art
Owing to the improved light emission efficiency and decreased price of Light Emitting Diodes (LEDs), LEDs have gained popularity in the general lighting market, which includes fluorescent lighting and incandescent lighting, as well as in the special lighting market, including portable devices, displays, cars, signal signs, and advertisement boards.
Also, optical wireless communication technology, as complimentary to RF technology, has attracted much interest due to the shortage of Radio Frequency (RF) bands, the possibility of interference between different radio communication technologies, increased demands for communication security, and the advent of an ultra-high ubiquitous communication environment of 4th Generation (4G) radio technology. In this context, many companies and research institutes are studying VLC using visible light LEDs.
VLC for transmitting information by light visible to the human eye offers the benefits of a wide bandwidth, free use, without restrictions, compared to wave communications, visibility of the destination or passage of light, and the resulting accurate detection of an information reception range. Therefore, VLC is reliable in terms of security and consumes low power. In this context, VLC can be applied to hospitals and airplanes where RF use is restricted and provide additional information services through an advertisement board. A VLC system will be described below.
FIG. 1A illustrates a conventional VLC system. The conventional VLC system includes LED or Laser Diode (LD) lamps 141, 142 and 143 for acting as lights and transmitting and receiving data by visible light, and communication devices 150 and 160 each having a visible transceiver module for transmitting and receiving data to and from the lamps 141, 142 and 143. The communication devices 150 and 160 can be a mobile terminal such as a portable phone or a Personal Digital Assistant (PDA), or a fixed terminal such as a desktop computer.
FIG. 1B illustrates a VLC-based peripheral interface system. In the VLC-based peripheral interface system, a communication device 170 like a laptop or a desktop that has a visible light transceiver module, a portable mobile terminal 180 such as a hand-held phone or a PDA, a peripheral device 190 like a printer, or a small digital device like a digital camera or an mp3 player communicate with one another by visible light. A VLC-based peripheral device interface guarantees security and is implemented with low power.
The VLC can be more efficient through convergence with other wired or wireless communication systems using different communication media. Among them, a VLC system for providing information by lighting inside a building in conjunction with Power Line Communication (PLC) will be described below in detail.
FIG. 2 illustrates a conventional communication system using PLC and VLC in combination. In FIG. 2, a conventional method for providing location-based information to a user over a lamp network by PLC is illustrated (see, for example, Korea Patent Publication No. 10-2005-71617 entitled “Illumination Light Communication Device mark, filed by Nakagawa, et al., on Apr. 23, 2005). In the conventional technology, power and information are simultaneously transferred via a power line 103. A lamp 131 connected to the power line 103 modulates information received via the power line 103 to a visible light signal and provides the modulated information to a user 133. In this illustrated example, the information may about a piece of art work 132 positioned in an area illuminated by the lamp 131.
FIG. 3 is a diagram illustrating a message exchange procedure between network entities in the conventional communication system using PLC and VLC illustrated in FIG. 2.
Referring to FIG. 3, a server 134 transmits information to lamps 131 forming a lamp network via a power line and the lamps 131 generate visible light signals by VLC. The conventional location-based service using a power line simply provides information about a fixed object to a mobile terminal, thus having limitations in information transmission.
Meanwhile, mobile communication terminals including portable phones, Personal Communications Services (PCSs), International Mobile Telecommunication-2000 (IMT-2000) terminals, and PDAs are equipped with various convenient functions such as a message transmission/reception function, a wireless Internet function, a schedule management function, a camera function, a music player function, an electronic dictionary function, and a navigation function in addition to a simple voice call function.
Among the convenient functions, a Global Positioning System (GPS)-based navigation function is used for indicating to a user a path and direction to a destination entered by the user. In general, since the navigation function is designed to provide information about the current location of a vehicle, it can search for a path based on map data stored in a database.
Beyond this vehicle navigation system, navigation for a walker as well as for a vehicle is under development. A pedestrian navigation device indicates a path to a destination to a user carrying the pedestrian navigation device and allows the user to monitor the user's progress along the path.
When a pedestrian enters a building or underground, however, the GPS-based navigation service is not available as GPS signals cannot be received. Accordingly, there exists a need for navigation inside a building along with the trend of increasing construction of large-scale building structures such as skyscrapers, huge shopping malls, and large underground arcades.